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An Ultrasonic Flowmeter with Broadband Transducers and Multiple-Frequency Signal Transmitter

IP.com Disclosure Number: IPCOM000201649D
Original Publication Date: 2010-Nov-17
Included in the Prior Art Database: 2010-Nov-17
Document File: 7 page(s) / 400K

Publishing Venue

Siemens

Related People

Juergen Carstens: CONTACT

Abstract

Due to environmental noise or system fluctuation, current ultrasonic flowmeters can be unstable in regard to the reading operation. In the worst case scenario, i.e. if the Signal-Noise-Ratio (SNR) drops below the respective limit, the flowmeters can even stop working. Usually, certain errors are displayed on the flowmeter. For example if the time-of-flight is not stable, a flashing letter such as F appears on the display of the flowmeter. A low SNR level may be caused by air bubbles or particles of any kind which disturb the measurement. Usually, the maximum limits of solids and gas in the fluid of flowmeters are between 1 and 12 percent. A low SNR level can also be caused by field electromagnetic interference, flow jitters and operation of pumps and valves. One current solution uses a zero crossing detector which determines a zero level crossing of a current pulse and monitors the amplitude to determine a pre-trigger level. However, the solution can only be used for the measurement error if the SNR is good and the received signal amplitude is only disturbed within a limited range. When severe interference lowers the SNR below a limit, the pre-trigger level can not be properly set to detect a unique zero crossing point. Thus, the flowmeter delivers false measurement results.

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An Ultrasonic Flowmeter with Broadband Transducers and Multiple-Frequency Signal Transmitter

Idea: Shunjie Fan, Ph.D., CN-Beijing; Bing Kong, Ph.D., CN-Beijing; Min Guo, CN-Beijing; Yue
Zhuo, Ph.D., CN-Beijing

Due to environmental noise or system fluctuation, current ultrasonic flowmeters can be unstable in regard to the reading operation. In the worst case scenario, i.e. if the Signal-Noise-Ratio (SNR) drops below the respective limit, the flowmeters can even stop working. Usually, certain errors are displayed on the flowmeter. For example if the time-of-flight is not stable, a flashing letter such as F appears on the display of the flowmeter. A low SNR level may be caused by air bubbles or particles of any kind which disturb the measurement. Usually, the maximum limits of solids and gas in the fluid of flowmeters are between 1 and 12 percent. A low SNR level can also be caused by field electromagnetic interference, flow jitters and operation of pumps and valves.

One current solution uses a zero crossing detector which determines a zero level crossing of a current pulse and monitors the amplitude to determine a pre-trigger level. However, the solution can only be used for the measurement error if the SNR is good and the received signal amplitude is only disturbed within a limited range. When severe interference lowers the SNR below a limit, the pre-trigger level can not be properly set to detect a unique zero crossing point. Thus, the flowmeter delivers false measurement results.

In another solution it is proposed for the ultrasonic flowmeter arrival time detection to code the input signals for narrowband transducers. Chip signals (linear sweeping from 0.9 MHz to 1.1 MHz) and combined two-frequency (0.9 MHz and 1.1 MHz) signals are used to improve the arrival time detection. However, the simulation results show that the improvement for narrowband transducers is very limited, since the response is almost exclusive at the center frequency.

Furthermore, the input signal energy is not increased at a given pulsing voltage in both solutions. To improve the SNR, the input energy to the sending transducer has to be increased. For this purpose several averaging methods are used to enhance the signal while eliminating the noise. One current method is the so-called ABM (Anti-Bubble Measuring) method which is used to achieve enhanced SNR and anti-bubble performance. When ultrasound propagation is interrupted by air bubbles, the received signal can not be discriminated from noises. The transmitted ultrasonic signal can be reconstructed by the synchronized summation of multiple received signals. Using the ABM method, the reliability of the measurement can be improved for different flows such as slurries, sludge, raw sewage and bubble-contained flow. Nevertheless, the method has disadvantages. The summation of multiple received si...